Sweetening hydrocarbons with dried chromium oxide



United States atent G SWEETENING HYDROCARBONS WITH DRIED CHROMIUM OXIDE Peter B. Murray, Swarthmore, Pa., assignor to Sun Oil Ityl'ompany, Philadelphia, Pa., a corporation of New ersey No Drawing. Filed Dec. 10, 1956, Ser. No. 627,142

6 Claims. (Cl. 208189) This invention relates to the conversion of mercaptans contained in hydrocarbon materials, and more particularly to a manner of refining petroleum fractions containing mercaptans.

It is frequently desirable to treat hydrocarbon materials such as petroleum fractions in order to convert mercaptans contained therein into a less objectionable form. Thus for example, straight run or cracked gasoline may be treated in order to eliminate the bad odor caused by mercaptans normally contained in such fractions. Also, petroleum fuel-oil compositons, forexample cracked gas oils, may be treated in order to convert mercaptans which, if not converted, react with copper during use of the fuel oil, the resulting copper mercaptides having unde sirable gel-forming properties.

In the conversion of mercaptans, for example to disulfides, by contact with a refining agent, it is desirable that the refining agent be, capable of treating a large amount of hydrocarbon material. The present invention is advantageous in providing a refining agent which is capable of providing highly satisfactory conversion of mercaptans, while retaining its activity for such conversion during treatment of large amounts of hydrocarbon materials. The invention is further advantageous in that the refining agent is susceptible to regeneration without excessive difficulty to restore its high activity for conversion of mercaptans.

The treating agent employed according to the invention comprises chromium oxide which hasbeen pretreated in a'special manner which is required for satisfactory results- The treating agent can consist essentially of solid chromium oxide or it can comprise chromium oxide associated with other materials. Preferably, the treating agent comprises chromium oxide associated with a solid porousgranular support or carrier. The treating agent is'subjected to'a drying operation prior to contacting with hydrocarbons containing mercaptans. The drying operation is essential, since it has been found that the life of the treating agent is disadvantageously short when the treating operation is not directly preceded by a drying, operation.

The drying operation can be conducted in any suitable manner. It may for example involve heating with or without the aid of reduced pressure, to vaporize water. A dry gas capable of taking up water vapor can if desired be contacted with the treating agent to remove water therefrom. The drying operation is preferably performed by subjecting the treating agent to temperatures above the boiling point of water at the pressure involved, though this feature is not essential if a drying gas is used for example. At atmospheric pressure, the temperature is preferably at least about 250 F. At subatmospheric pressures, lower temperatures, e.g. down to 200 F. or lower can be employed. The duration of the drying is preferably suflicient to remove a major proportion of the water normally contained in the treating agent in equilibrium with the atmosphere. The duration is preferably at least one half hour, though shorter times are suflicient under severer drying conditions. Usually, not more 10' ployed if desired.

It is further preferred according to the invention that the treating agent be subjected to a further heating operation which is carried out in the presence of gaseous oxygen. Any suitable oxygen containing gas, e.g. air, can be employed. The temperature of such contacting with oxygen is preferably within the approximate range from 250 F. to 1500 F., and more preferably at least- 750 F. The drying step and the contacting with oxygencan be conducted: in a single operation, or if desired in separate operations comprising a drying step at relatively low temperature followed by a heating step at higher temperature with introduction of gaseous oxygen into the heating zone. The time of heating in the pres ence of oxygen is preferably within the approximate range from one hour to ten hours, though other periods can be employed if desired.

Preferably the treating agent according to the invention is in a low state of hydration as a result of the pretreatment, since the absence of water contributes beneficiallyto the life and activityof the treating agent for conversion of mercaptans. It is also preferred that thechromium in the treating agent should comprise large proportions of hexavalent chromium,'present for example as chromium trioxide, since such chromium is generally more active for the purpose of the invention than chromium in lower valence states. Preheating in the presence of oxygen to temperatures of at least about 750 F. for example is preferred in that it favors the formation of hexavalent chromium.

It has been found that the treating agent according to; theinvention'has very high activity and long life in the conversion of mercaptans. Thus for example 2000 bbls. of straight run gasoline or more can typically be rendered sweet to the doctor'test per ton of treating agent containing 5% chromium trioxide. Treating agents containing greater proportions of chromium trioxide have even longer life.

The hydrocarbon charged'to the treated operation preferably contains little if any water, since Water tends to decrease the life of the treating agent. Preferably therefore the hydrocarbon charge is dried prior to the treating operation, in those cases where the charge ordinarily con-- tains excessive amounts of water. Any suitable known method for dehydration of hydrocarbons can be employed prior to the treating step. Thus for example cal-- cium chloride or other suitable known drying agent can be employed.

The hydrocarbon charge should be as free aspossibleof'strong acids such as mineral acids. Thus generally the content of mineral acidity should be less than ppm, and preferably is as close to zero as possible. Accordingly, the charge should not be treated with a mineral acid prior to the treating operation according to the invention. Excessive amounts of mineral acid in the charge result in rapid deactivation of the treating agent, and also render the treating agent more diificult to regenerate.

The process according to the invention is carried out at a temperature below about F. Excessively high temperatures should be avoided in order to avoid decomposition and darkening of the hydrocarbon charge and also of the treating agent. The process is carried out in liquid phase, and elevated pressure is employed if necessary, though operation at atmospheric pressure is preferred. Preferably, the process is carried out by percolating the hydrocarbon charge through a stationary bed of the treating agent, though other contacting methods as well known in the art can be employed if desired.

Thejpmcess according to the invention'is believed to involve oxidation of mercaptans to form disuliides. The oxygen necessary for this oxidation is supplied by the oxygen associated with chromium in the treating agent.

. Qther; 1 oxidation reactions which .occur .in the, presence. of;,excess1ve amounts of gaseous oxygen aregenejrally oxygen, and affirmative removal'of oxygen is generally.

notnecessary.

- *Any suitable support for the chromium oxide can be employed: Examples'of suitable supportsare silica. gel, alumina, silica-alumina compositions, bauxite, clay, activated carbon, asbestos, kieselguhr, magnesium oxide; pumice, cm; In' the case of bauxite, either ordinary bauxite or 'highor low-iron bauxites; as obtained in magnetic, separation of bauxite can be employed. Any suitable manner of associating chromium oxide with the support can be employed, e.g. coprecipitation," impregnation; e'tc. Thus forexample the support and the chromium compound can be coprecipitated, from an aqueous solution, or the support, which may have been previously precipitated from an aqueous solution, ,1 can be impregnated with an' aqueous solution of a chromium compound,.etc. Examples of chromium compounds, aqueous solutions of which can be employed in precipitation or impregnation processes, are chromium oxides, e.g.,chro-' mium trioxide (chromic acid), and various compounds convertible thereto by heating, e.g. chromium acetate,

chromium chloride, chromium sulfate, ammonium chromate, ammonium dichromate. 1 a I 1 a The treating agent according to the invention can be regenerated, after use 'in conversion of mercaptans, by contacting with 'steam or other inert vaporous or gaseous material to remove adsorbed hydrocarbons, and' subsequently drying the treating agent or heating with oxygen in the manner previously described with regard to original preparation of the treating agent. 4 p 1 Little or no hydrogen sulfide is formed in the process according to the invention, the process involving oxidation of mercaptans to disulfides rather than decomposition of organic sulfur compounds to form hydrogen sulfides. i

' The amount of chromium oxide contained on the sup-,

port can vary widely. In general, greater amounts of chromium oxide provide more satisfactory operation, longer life, etc. In the case of coprecipitatcd treating agents, as much as 70 weight percent of chromium oxide can if desired be incorporated in the treating agent. In the case of treating agents formed by impregnation, it is generally not feasible to incorporate more than 40 weight percent of chromium trioxide. Generally, it will be desired to incorporate at least one weight percent of chromium trioxide.

The support material, such as a silica-alumina composition, can be separately activated if desired by heating to a temperature for example withinthe. approximate range from 1100 to l300 Fffor 2' to 16 hours in the presence of steam and air, the amount of steam in the activating gas being Within the approximate range from '3 to 10 volume percent.

r If desired, other metals can be associated with the chromium in the treating agent, for example strontium, iron, etc. However, chromium oxide provides highly satisfactory results in the absence of other metals.

. The following example illustrates the invention:

Example I t A treating agent was prepared containing coprecipitated silica" and alumina impregnated with- 5' weight percent re onia s-9 The Weight pr ponige 9f a li e t alumina'was 9 to 1. The silica-alumina composite was prepared according to standard procedure for preparation of synthetic silica-alumina cracking catalysts, as well known in the art, and the composite, which was about '10 to 20 mesh (United States sieve series), conformed to standard cracking catalysts.

The impregnation was performed by adding an aqueous solution of chromium trioxide to the silica-alumina composite in proportions equivalent to 56 milliliters of solution per 100 grams of composite, the weight ratio of chromium trioxide on the anhydrous basis to the composite being 4.92100. A portion of the impregnated" material was pretreated by heating to 9001000 F. for

- one hour, while blowing air across the material. Di-

rectly following this pretreatment, 60 cc. of the-impreghated composite were employed in a stationary bed as a treating agent for straight run gasoline containing essentially no mineral acidity and containing 0.006 weight percent of mercaptan sulfur.

The gasoline was passed through the bed at room temperature and atmospheric pressure and a liquid hourly space velocity of 15 volumes per volume of catalyst :bed per hour. Three liters of doctor sweet product were obtained in 3 /3 hours. The treatment was then terminated. However, there was no sign of deactivation of' the treating agent at the time of termination, indicating that considerably larger amounts of doctor sweet product could be obtained.

7 i For comparison, another portion of the impregnated material, after an initial drying at 250 F. for 2 hours,

was allowed to stand exposed to the atmosphere at room temperature for several days, thereby becoming hydrated by adsorption of water from the atmosphere. The treating agent was then used to treat another portion of the same straight run gasoline under the same conditions as in the case of the other portion of the impregnated material. The following results were obtained:

- r Liters of Treating Agent Pretreatment Doctor V Sweet Product Heated with oxygen, 900-1,000 F., 2 hours 3 Exposed to atmosphere at room temperature I 1 This table shows that it is essential, to obtain good tacting with hydrocarbons.

Drying at lower temperatures in the absenceof added oxygen is satisfactory in some instances. ample, drying at 250 F. for 2 hours is effective, if directly followed by hydrocarbon contacting, to provide longer life than in the case of an undried treating agentk fResults generally similar to those obtained 'inythis example are obtained with other treating agents within the scope of the invention, e.g. bauxite impregnated with aqueous chromium nitrate and heated with added air to 1400 F. for'5 hours to obtain a composition containing 25 welght percent of chromium oxide, silica gel impregnated with aqueous ammonium chromate'and heated in therabsence of added air to 400 F. for 15 hours, care being taken to avoid too rapid'heating and spontaneous thermal decomposition, 'to obtain a compo sition containing 10 weight percent of chromium oxide,

etc. I t

The low mineral acidity of the gasoline treated is an essential feature. In treating,under conditions described in Example I, a gasoline containing 0.006 weight percent (about 60 p.p.m.) of mercaptan sulfur and ppm, for example, of sulfuric acid, the amount of doctor sweet gasoline obtainable is much less than that obtained in Example I, and theregeneration of the treating agent is 'also'more difficult. a Preferably,'the amount of hexavalent chromium in the treating agent is about 35 to 1 00 weight percent based Thus, for exon total chromium, and more preferably at least about 50 weight percent. Thus, for example, under the conditions of Example I, superior sweetening efiect and life are obtained with 50 percent hexavalent chromium than with 25 percent.

The hydrocarbon charge stock which is refined according to the invention generally contains only a small amount of mercaptans. Typically, the amount is within the approximate range from 0.0005 to 0.05 weight percent, though other amounts are present in some instances.

The invention claimed is:

1. Process for sweetening hydrocarbons which comprises contacting hydrocarbons containing mercaptans and containing less than about 100 ppm. of mineral acidity in liquid phase at a temperature less than about 140 F. with a solid refining agent consisting essentially of material selected from the group consisting of dried chromium oxide and dried chromium oxide associated with a solid granular support, said refining agent containing 35 to 100% hexavalent chromium based'on total chromium, thereby to selectively convert mercaptans to disulfides.

2. Process according to claim 1 wherein said refining agent is previously dried at a temperature of at least about 200 F. and above the boiling point of water at the pressure employed.

3. Process according to claim 1 wherein said refining agent is previously contacted with gaseous oxygen at a temperature within the approximate range from 750 F. to 1500" F.

4. Process according to claim 1 wherein the chromium oxide is supported on a solid porous carrier.

5. Process according to claim 1 wherein said hydrocarbons are a gasoline fraction.

6. Process according to claim 1 wherein said hydrocarbons are a petroleum fuel oil fraction.

References Cited in the file of this patent UNITED STATES PATENTS 10,055 Brown Sept. 27, 1853 81,071 'De Gerbeth Aug. 18, 1868 190,762 Jenny May 15, 1877 648,048 Frasch May 8, 1900 713,475 Mims Nov. 11, 1902 1,110,925 Greenstreet Sept. 15, 1914 1,318,061 Ellis Oct. 7, 1919 1,590,965 Downs June 29, 1926 2,325,115 Eglolf July 27, 1943 2,346,734 Dempsey Apr. 18, 1944 2,351,094 Blaker June 13, 1944 2,357,691 Ruthrufi Sept. 5, 1944 FOREIGN PATENTS 143,193 Great Britain Feb. 3, 1921 

1. PROCESS FOR SWEETENING HYDROCARBONS WHICH COMPRISES CONTACTING HYDROCARBONS CONTAINING MERCAPTANS AND CONTAINING LESS THAN ABOUT 100 P.P.M. OF MINERAL ACIDITY IN LIQUID PHASE AT A TEMPERATURE LESS THAN ABOUT 140*F. WITH A SOLID REFINING AGENT CONSISTING ESSENTIALLY OF MATERIAL SELECTED FROM THE GROUP CONSISTING OF DRIED CHROMIUM OXIDE AND DRIED CHROMIUM OXIDE ASSOCIATED WITH A SOLID GRANULAR SUPPORT, SAID REFINING AGENT CONTAINING 35 TO 100% HEXAVALENT CHROMIUM BASED ON TOTAL CHROMIUM, THEREBY TO SELECTIVELY CONVERT MERCAPTANS TO DISULFIDES. 